Regarding the issue of large frequency converters being able to drive small motors
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A variable-frequency drive system is a system in which an inverter supplies power to control a motor that drives mechanical equipment. The interaction between the inverter and the motor is crucial for the operation of this system. So, if the rated current of the motor is lower than that of the inverter, what size of motor can the inverter actually control? The requirements for controlling the operation of low-power motors using high-power frequency converters can be divided into two scenarios: In the first scenario, the frequency converter operates in vector control mode, and in this case the rated current of the motor should be at least 25% of the rated current of the frequency converter. The larger the difference between the motor’s rated current and the converter’s rated current, the lower the accuracy of the actual current sensing circuit, and the worse the performance of vector control. For high-precision vector control inverter systems equipped with speed encoders, high control performance is generally required; in such cases, it is recommended that the rated current of the inverter be at least 50% of the motor’s rated current. Changhui Instruments, yunrun.com.cn. The second application scenario is when the frequency converter operates in U/F control mode. In such systems, the control requirements are generally not high; as a result, there are few restrictions on the matching between the motor’s rated current and that of the converter. Even motors with very low power levels can be controlled by a frequency converter. However, it must be noted in this case that when a motor with very low power is operated under the control of a converter with very high power, the extremely low motor current prevents the automatic identification of the motor parameters from being carried out. For the same reason, it is difficult for the inverter to provide reliable motor overload protection at this time; other motor overload protection devices must be used for such protection.
High-power frequency converters can control low-power motors, but several factors need to be taken into account. During vector control, the motor current should be at least 25% of the inverter current, and ideally 50%. In U/F control mode, the matching constraint between motor current and inverter current is not severe, but it may affect automatic parameter recognition and overload protection, requiring additional protective devices. .
In variable frequency drive systems, the cooperation between the inverter and the motor is indeed crucial to the system. When considering the use of high-power inverters to control low-power motors, there are two scenarios along with their corresponding requirements: Vector control mode: In this mode, the rated current of the motor should be at least 25% of the rated current of the inverter. If the difference between the motor’s rated current and the inverter’s rated current is too large, the accuracy of the actual current sensing circuit decreases, which in turn affects the performance of vector control. For high-precision vector control inverter systems equipped with speed encoders, higher control performance requirements are typically expected. In this case, it is recommended that the rated current of the frequency converter be at least 50% of the motor’s rated current. U/F (voltage/frequency) control mode: In the U/F control mode, there are virtually no restrictions on the combination of the motor’s rated current and the inverter’s rated current; even motors with very low power levels can be controlled by the inverter. However, when a motor with very low power is controlled by an inverter with very high power, the inverter may be unable to automatically identify the motor parameters due to the extremely low motor current. Similarly, in this case, it is difficult for the inverter to provide reliable motor overload protection; therefore, other motor overload protection devices need to be used to achieve this function. In summary, the size of motor that a frequency converter can control depends on its control mode and the specific requirements for integration. In vector control mode, there is a certain proportional relationship between the motor’s rated current and the inverter’s rated current, in order to ensure the performance and stability of the system. In the U/F control mode, although the combination of motor size and inverter power is more flexible, attention may need to be paid to motor parameter identification and overload protection. In practical applications, the appropriate control mode and configuration should be selected based on specific requirements and conditions, to ensure the proper operation and high efficiency of the variable frequency drive system.